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A. Ahmed

Publications and source records attributed to A. Ahmed.

At least 19 recordsLinked to original sources
arXiv2026

From Cluster Core to Splashback: Linking Dynamical Structure to Multidimensional Galaxy Evolution in the Coma Cluster

We investigate galaxy evolution across the full dynamical structure of the Coma cluster using the GalWCat19 spectroscopic cluster catalog combined with SDSS-based value-added galaxy properties. We measure a splashback radius of $R_{sp} = 2.94 \pm 0.16~h^{-1}\, Mpc$. Using specific star formation rate (sSFR), color offset from the red sequence ($\Delta(g-r)_{RS}$), and bulge-to-total ratio ($B/T$) as independent diagnostics, we find a coherent environmental transition from quiescent, red, bulge-dominated galaxies in the cluster core to increasingly star-forming, blue, disk-dominated populations at larger radii. We further introduce a three-dimensional framework in the joint $(\log sSFR, \Delta(g-r)_{RS}, B/T)$ space and develop a peak-based classification scheme that extends beyond traditional one-dimensional galaxy classifications. This framework identifies two dominant populations: red, quiescent, bulge-dominated galaxies, which account for $51\%$ of the joint-analysis sample, and blue, star-forming, disk-dominated galaxies, which account for $29\%$. The remaining $\sim20\%$ of galaxies occupy transitional or mixed states that connect these two principal populations. The relative fractions of these populations change strongly near the splashback radius, where the red, quiescent, bulge-dominated population declines rapidly and the blue, star-forming, disk-dominated population becomes increasingly dominant. These results show that the splashback boundary is not only a dynamical boundary, but also a critical evolutionary transition zone. Overall, our findings suggest that galaxy evolution in Coma is not a purely binary transformation, but instead proceeds through continuous multidimensional pathways in which star formation quenching, color evolution, and morphological transformation occur on different timescales while remaining closely linked to the cluster dynamical structure.

astro-ph.GA↗
arXiv2026

Characterizing Human-Likeness in AI Generated Poetry: A Zero-shot Classification Study

With the advancement of AI technologies, Generative AI (GenAI) and human written text have become nearly indistinguishable. Additionally, the global standardization of AI chatbots made academic malpractice more frequent. Furthermore, existing research indicates GenAI poems are the most difficult to distinguish even without any modification thus, GenAI poems are naturally deemed human-like by modern detectors. However, the objectivity of such dissertations needs to be verified against modern detection tools but the subjectivity of poetry and the black-box nature of the modern LLMs (Large Language Models) architectures made verification of such work quite complicated. Hence, the main objective of the research is to deduce the attributes of English poetry that contribute classification and misclassification of both human and AI poems and provide corroborating or contradicting evidence to the poetry distinguishability claim. For such characterizations, we propose a Zero-shot detection pipeline with a dataset consisting of both human and AI poems to verify the distinguishability of human and AI creation and extract the aforementioned crucial attributes for accurate classification. Extraction of such attributes provides benefits in two ways: firstly, it reduces the margin of training needed as only the poems based on misclassifying attributes need to be trained and fine tuned and finally provides a critical insight to the GenAI detection dilemma to strengthen the modern detection pipelines.

cs.CL↗
arXiv2026

Structure and Evolution of Multi-Cluster within Galactic Disc: Gaia DR3 Insights into Eight Open Clusters

In this study, we present a comprehensive analysis of the structural, astrophysical, and dynamical properties of eight open clusters: NGC 559, NGC 1817, NGC 2141, NGC 7245, Ruprecht 15, Ruprecht 137, Ruprecht 142, and Ruprecht 169, using precise astrometric and photometric data from Gaia Data Release 3. By fitting the King model to the radial density profiles, we determined the structural parameters of the clusters, including core and limiting radii, which were found to range from 3.07 to 16.21 arcmin and from 9.97 to 25.97 arcmin, respectively. Fundamental astrophysical parameters were derived by fitting PARSEC isochrones to the colour-magnitude diagrams. The results show that the clusters have logarithmic ages between 7.95 and 9.34, metallicities in the range 0.007 to 0.015, and heliocentric distances between 1640 and 5203 pc. The total stellar masses of the clusters were estimated to lie between 257 and 1916 solar masses. For most of the clusters, the mass function slopes are consistent with the Salpeter initial mass function. Our dynamical analysis indicates that all clusters, except Ruprecht 15, are dynamically relaxed. In addition, the spatial distribution and the bimodal structure observed in the radial density profile of NGC 7245 provide strong evidence that this object is a binary cluster candidate. Finally, kinematic analysis and orbit integrations demonstrate that all clusters exhibit dynamical properties fully consistent with membership in the Galactic thin disc.

astro-ph.GA↗
arXiv2026

Tracing the Galactic Disk with Gaia DR3: A Deep Study of Berkeley 17, 18, and 39 Open Star Clusters

We report a detailed investigation of three intermediate-to-old age open clusters, Berkeley 17, Berkeley 18, and Berkeley 39, utilizing precise astrometric and photometric data from Gaia DR3. Cluster membership was robustly determined through a probabilistic proper-motion analysis, yielding statistically significant samples of 600, 1042, and 907 stars, respectively. From the mean parallaxes of these members, we determine astrometric distances ranging from approximately 3.40 kpc for Berkeley 17 to 5.80 kpc for Berkeley 18. Isochrone fitting applied to the decontaminated color-magnitude diagrams constrains the cluster ages to 9.12 +/- 1.00 Gyr, 3.36 +/- 0.50 Gyr, and 5.10 +/- 0.50 Gyr, respectively. Interstellar reddening spans a wide range, from E(B-V) = 0.17 mag in Berkeley 39 to 0.58 mag in Berkeley 17. Structural parameters derived from King model fits to the radial density profiles, combined with mass function analyses, indicate that the clusters are dynamically relaxed systems with mass distributions broadly consistent with the canonical Salpeter slope. Our kinematic analysis reveals that Berkeley 17, Berkeley 18, and Berkeley 39 are part of the outer disk population.

astro-ph.GA↗
arXiv2025

Exploring the Structure and Evolution of Four Young Open Clusters Near the Galactic Mid-plane via Gaia DR3

We present a comprehensive analysis of four young open clusters, NGC 663, NGC 2301, NGC 2384, and NGC 7510, utilizing high-precision astrometric and photometric data from Gaia DR3. Cluster membership was determined using the UPMASK algorithm, resulting in probable member counts ranging from 337 to 1498 across the clusters. Bayesian MCMC isochrone fitting yielded cluster ages in the range $\log t \sim 7.0$ -$8.15$, with uncertainties of $\sim 0.11$-$0.18$. Reddening values ranged from $E(B-V)=0.093$ mag in NGC 2301 to $1.24$ mag in NGC 7510, consistent with their positions near the Galactic plane. The stellar mass function slopes ($\alpha \approx 2.00$-$2.26$) closely match the Salpeter IMF, with total stellar masses spanning nearly an order of magnitude, from $\sim 486\,M_\odot$ in NGC 2301 to $\sim 3584\,M_\odot$ in NGC 663. Dynamical relaxation times indicate that only NGC 2301 ($\tau \approx 10.00$) and NGC 2384b ($\tau \approx 2.03$) are dynamically relaxed; the others remain dynamically evolving. Orbital integrations in the MWPotential2014 model reveal nearly circular Galactic orbits with very low eccentricities ($e \approx 0.003$-$0.014$) and small vertical distances ($Z_{\rm max} < 0.142$ kpc), confirming their confinement to the thin disk. SED and kinematic analysis show that NGC 2384a and NGC 2384b are separated by $\sim 0.55$ kpc, indicating an optical pair.

astro-ph.GA↗
arXiv2025

Galaxy Cluster Detection and Dynamical Analysis in the VIPERS High-Redshift Spectroscopic Survey

We present a dynamical analysis of galaxy clusters identified in the VIPERS spectroscopic survey within the redshift range 0.5 <= z <= 1.2. Cluster candidates were first detected as overdense regions in redshift space through the Finger-of-God (FoG) effect, and cluster membership was assigned using the GalWeight technique within the FoG-GalWeight methodology developed by our team. For each cluster, we derived the virial radius (R200), velocity dispersion (sigma200), and virial mass (M200) using the virial mass estimator. We identified ten VIPERS clusters spanning a mass range of 0.59 x 10^14 <= M200/(h^-1 Msun) <= 4.32 x 10^14 and velocity dispersions of 360 <= sigma200 <= 900 km s^-1. We cross-matched the VIPERS clusters with published catalogs and found at least one matching system for each cluster, offering external validation for our detections. We investigated the velocity dispersion-mass relation for these systems and obtained log(sigma200) = (2.73 +/- 0.06) + (0.36 +/- 0.18) log(M200), with an intrinsic scatter of sigma_int = 0.04 +/- 0.07. The derived relation is consistent with theoretical predictions from N-body and hydrodynamical simulations, confirming the reliability of the FoG-GalWeight methodology and the robustness of the virial mass estimator. Our findings demonstrate that the velocity dispersion can serve as a reliable and direct proxy for cluster mass, even at high redshift, without requiring additional dynamical mass modeling.

astro-ph.CO↗
arXiv2024

An in-depth analysis of the differentially expanding star cluster Stock 18 (Villafranca O-036) using Gaia DR3 and ground-based data

(ABRIDGED) CONTEXT: The Villafranca project is combining Gaia data with ground-based surveys to analyze Galactic stellar groups with OB stars. AIMS: We want to analyze Stock 18 within the Villafranca project, a very young stellar cluster with a symmetrical and compact H II region around it. METHODS: We analyze the core, massive-star population, extinction, distance, membership, internal dynamics, density profile, age, IMF, total mass, stellar variability, and Galactic location of Stock 18 with Gaia data and ground-based spectroscopy. RESULTS: Stock 18 is a very young (~1.0 Ma) cluster located at a distance of 2.91+-0.10 kpc dominated by the GLS 13 370 system, whose primary is an O9 V star. We propose that Stock 18 was in a very compact state (~0.1 pc) about 1.0 Ma ago and that most massive stars were ejected at that time without significantly affecting the less massive stars as a result of multi-body dynamical interactions. Given its age close to 1.0 Ma, the dynamical interactions took place very soon after massive star formation. Well defined expanding stellar clusters have been observed before but none as young as this one. The IMF is top heavy but if we discard the ejected ones it becomes nearly canonical. Therefore, this is another example in addition to the one we previously found (the Bermuda cluster) of (a) a very young cluster with an already evolved PDMF (b) that has significantly contributed to the future population of free-floating compact objects. If confirmed in more clusters, the number of such compact objects may be higher in the Milky Way than previously thought. Stock 18 has a variable extinction with an average value of R_5495 higher than the canonical one of 3.1. The cluster is above our Galactic mid-plane and has a distinct motion with respect to its surrounding old population, which is possibly an influence of the Perseus spiral arm.

astro-ph.GA↗
arXiv2024

Crowdsourcing with Enhanced Data Quality Assurance: An Efficient Approach to Mitigate Resource Scarcity Challenges in Training Large Language Models for Healthcare

Large Language Models (LLMs) have demonstrated immense potential in artificial intelligence across various domains, including healthcare. However, their efficacy is hindered by the need for high-quality labeled data, which is often expensive and time-consuming to create, particularly in low-resource domains like healthcare. To address these challenges, we propose a crowdsourcing (CS) framework enriched with quality control measures at the pre-, real-time-, and post-data gathering stages. Our study evaluated the effectiveness of enhancing data quality through its impact on LLMs (Bio-BERT) for predicting autism-related symptoms. The results show that real-time quality control improves data quality by 19 percent compared to pre-quality control. Fine-tuning Bio-BERT using crowdsourced data generally increased recall compared to the Bio-BERT baseline but lowered precision. Our findings highlighted the potential of crowdsourcing and quality control in resource-constrained environments and offered insights into optimizing healthcare LLMs for informed decision-making and improved patient care.

cs.CL↗
arXiv2022

the impact of the AGN and the torus properties on the evolution of spiral galaxies

For spiral galaxies, the active galactic nucleus (AGN) and some physical parameters that concern the host galaxy such as spiral arm radius and density can play an important role in the morphological evolution of these galaxies. Considering the gravitational effect of the central black hole as a feeding mechanism, the gas flows from spiral arms to the accretion disk. Accordingly, we constructed our approach and derived an equation for the AGN luminosity that depends on parameters such as the black hole mass and the spiral arm density. The galaxy samples were taken from a catalog of type 1 AGN from SDSS-DR7. In our model, we present the relation between the AGN luminosity and the black hole mass depending on the above physical parameters. We also investigated the relation between the black hole mass and the star formation rate for the galaxy sample. The physical properties of the torus, such as the spiral arm radius, density, the torus length, and the gas mass, and the star formation rate, were explained in terms of the variation of the AGN luminosity. These properties are more effective in the evolutionary scenario of the spiral galaxy. Relative to the variation of the AGN luminosity, the evolutionary track is different based quantitatively on the star formation rate. In which the variation in the star formation rate is positively correlated with the AGN luminosity.

astro-ph.GA↗
arXiv2022

Online Feedback Optimization of Compressor Stations with Model Adaptation using Gaussian Process Regression

Online Feedback Optimization is a method used to steer the operation of a process plant to its optimal operating point without explicitly solving a nonlinear constrained optimization problem. This is achieved by leveraging a linear plant model and feedback from measurements. However the presence of plant-model mismatch leads to suboptimal results when using this approach. Learning the plant-model mismatch enables Online Feedback Optimization to overcome this shortcoming. In this work we present a novel application of Online Feedback Optimization with online model adaptation using Gaussian Process regression. We demonstrate our approach with a realistic load sharing problem in a compressor station with parametric and structural plant-model mismatch. We assume imperfect knowledge of the compressor maps and design an Online Feedback Optimization controller that minimizes the compressor station power consumption. In the evaluated scenario, imperfect knowledge of the plant leads to a 5\% increase in power consumption compared to the case with perfect knowledge. We demonstrate that Online Feedback Optimization with model adaptation reduces this increase to only 0.8%, closely approximating the case of perfect knowledge of the plant, regardless of the type of mismatch.

eess.SY↗
arXiv2022

Quality Control of Mass-Produced GEM Detectors for the CMS GE1/1 Muon Upgrade

The series of upgrades to the Large Hadron Collider, culminating in the High Luminosity Large Hadron Collider, will enable a significant expansion of the physics program of the CMS experiment. However, the accelerator upgrades will also make the experimental conditions more challenging, with implications for detector operations, triggering, and data analysis. The luminosity of the proton-proton collisions is expected to exceed $2-3\times10^{34}$~cm$^{-2}$s$^{-1}$ for Run 3 (starting in 2022), and it will be at least $5\times10^{34}$~cm$^{-2}$s$^{-1}$ when the High Luminosity Large Hadron Collider is completed for Run 4. These conditions will affect muon triggering, identification, and measurement, which are critical capabilities of the experiment. To address these challenges, additional muon detectors are being installed in the CMS endcaps, based on Gas Electron Multiplier technology. For this purpose, 161 large triple-Gas Electron Multiplier detectors have been constructed and tested. Installation of these devices began in 2019 with the GE1/1 station and will be followed by two additional stations, GE2/1 and ME0, to be installed in 2023 and 2026, respectively. The assembly and quality control of the GE1/1 detectors were distributed across several production sites around the world. We motivate and discuss the quality control procedures that were developed to standardize the performance of the detectors, and we present the final results of the production. Out of 161 detectors produced, 156 detectors passed all tests, and 144 detectors are now installed in the CMS experiment. The various visual inspections, gas tightness tests, intrinsic noise rate characterizations, and effective gas gain and response uniformity tests allowed the project to achieve this high success rate.

physics.ins-det↗
arXiv2021

Performance of a Triple-GEM Demonstrator in $pp$ Collisions at the CMS Detector

After the Phase-2 high-luminosity upgrade to the Large Hadron Collider (LHC), the collision rate and therefore the background rate will significantly increase, particularly in the high $η$ region. To improve both the tracking and triggering of muons, the Compact Muon Solenoid (CMS) Collaboration plans to install triple-layer Gas Electron Multiplier (GEM) detectors in the CMS muon endcaps. Demonstrator GEM detectors were installed in CMS during 2017 to gain operational experience and perform a preliminary investigation of detector performance. We present the results of triple-GEM detector performance studies performed in situ during normal CMS and LHC operations in 2018. The distribution of cluster size and the efficiency to reconstruct high $p_T$ muons in proton--proton collisions are presented as well as the measurement of the environmental background rate to produce hits in the GEM detector.

physics.ins-det↗
arXiv2021

Modeling the triple-GEM detector response to background particles for the CMS Experiment

An estimate of environmental background hit rate on triple-GEM chambers is performed using Monte Carlo (MC) simulation and compared to data taken by test chambers installed in the CMS experiment (GE1/1) during Run-2 at the Large Hadron Collider (LHC). The hit rate is measured using data collected with proton-proton collisions at 13 TeV and a luminosity of 1.5$\times10^{34}$ cm$^{-2}$ s$^{-1}$. The simulation framework uses a combination of the FLUKA and Geant4 packages to obtain the hit rate. FLUKA provides the radiation environment around the GE1/1 chambers, which is comprised of the particle flux with momentum direction and energy spectra ranging from $10^{-11}$ to $10^{4}$ MeV for neutrons, $10^{-3}$ to $10^{4}$ MeV for $γ$'s, $10^{-2}$ to $10^{4}$ MeV for $e^{\pm}$, and $10^{-1}$ to $10^{4}$ MeV for charged hadrons. Geant4 provides an estimate of detector response (sensitivity) based on an accurate description of detector geometry, material composition and interaction of particles with the various detector layers. The MC simulated hit rate is estimated as a function of the perpendicular distance from the beam line and agrees with data within the assigned uncertainties of 10-14.5%. This simulation framework can be used to obtain a reliable estimate of background rates expected at the High Luminosity LHC.

physics.ins-det↗
arXiv2020

Interstrip Capacitances of the Readout Board used in Large Triple-GEM Detectors for the CMS Muon Upgrade

We present analytical calculations, Finite Element Analysis modeling, and physical measurements of the interstrip capacitances for different potential strip geometries and dimensions of the readout boards for the GE2/1 triple-Gas Electron Multiplier detector in the CMS muon system upgrade. The main goal of the study is to find configurations that minimize the interstrip capacitances and consequently maximize the signal-to-noise ratio for the detector. We find agreement at the 1.5--4.8% level between the two methods of calculations and on the average at the 17% level between calculations and measurements. A configuration with halved strip lengths and doubled strip widths results in a measured 27--29% reduction over the original configuration while leaving the total number of strips unchanged. We have now adopted this design modification for all eight module types of the GE2/1 detector and will produce the final detector with this new strip design.

physics.ins-det↗
arXiv2020

Study of transient plasma stream using Time-Integrated Spectroscopic Technique

Time integrated spectroscopic measurements are carried out to characterize transient plasma stream produced in a coaxial pulsed plasma accelerator. This method allows the estimation of different plasma parameters and its evolution with time. It also provides information on the existence of different excited states from the spectral emissions of plasma. Using Argon as the discharge medium, the electron density estimated from Stark broadened line profiles gives a peak value $\sim 5 \times 10^{21} m^{-3}$ at a discharge voltage of 15 kV and the flow velocity of the plasma stream is measured to be $\sim (22 + 5)$ Km using Doppler shift method. Assuming p-LTE model, the electron excitation temperature is found to be $\sim 0.88$ eV using Boltzmann plot method. A temporal evolution of the plasma stream and its characteristic variation is studied from a time of $50 μs-300 μs$ in steps of $50 μs$ by adjusting delay time in the triggering. Analysis of different spectral lines shows the existence of some metastable states of Ar II having a long lifetime. The evolution of different Ar II transitions to metastable and non-metastable lower levels is observed for different time frame. The temporal evolution study shows a decrease in electron density from $1.96 \times 10^{21} m^{-3}$ to $1.23 \times 10^{20} m^{-3}$ at $300 μs$ after the initiation of plasma formation. A decrease in excitation temperature from 0.86 eV to 0.72 eV is observed till $250 μs$ and then again rises to 0.77 eV at $300 μs$

physics.plasm-ph↗
arXiv2019

An ultra-wide bandwidth (704 to 4032 MHz) receiver for the Parkes radio telescope

We describe an ultra-wide-bandwidth, low-frequency receiver ("UWL") recently installed on the Parkes radio telescope. The receiver system provides continuous frequency coverage from 704 to 4032 MHz. For much of the band (~60%) the system temperature is approximately 22K and the receiver system remains in a linear regime even in the presence of strong mobile phone transmissions. We discuss the scientific and technical aspects of the new receiver including its astronomical objectives, as well as the feed, receiver, digitiser and signal-processor design. We describe the pipeline routines that form the archive-ready data products and how those data files can be accessed from the archives. The system performance is quantified including the system noise and linearity, beam shape, antenna efficiency, polarisation calibration and timing stability.

astro-ph.IM↗
arXiv2017

Video Synopsis Generation Using Spatio-Temporal Groups

Millions of surveillance cameras operate at 24x7 generating huge amount of visual data for processing. However, retrieval of important activities from such a large data can be time consuming. Thus, researchers are working on finding solutions to present hours of visual data in a compressed, but meaningful way. Video synopsis is one of the ways to represent activities using relatively shorter duration clips. So far, two main approaches have been used by researchers to address this problem, namely synopsis by tracking moving objects and synopsis by clustering moving objects. Synopses outputs, mainly depend on tracking, segmenting, and shifting of moving objects temporally as well as spatially. In many situations, tracking fails, thus produces multiple trajectories of the same object. Due to this, the object may appear and disappear multiple times within the same synopsis output, which is misleading. This also leads to discontinuity and often can be confusing to the viewer of the synopsis. In this paper, we present a new approach for generating compressed video synopsis by grouping tracklets of moving objects. Grouping helps to generate a synopsis where chronologically related objects appear together with meaningful spatio-temporal relation. Our proposed method produces continuous, but a less confusing synopses when tested on publicly available dataset videos as well as in-house dataset videos.

cs.CV↗